In a magnetic field, one of the magnetic layers of such a junction, traversed by a current of greater density than a so-called critical density, is the site of an oscillation of its magnetization vector. This oscillation results from the ferromagnetic resonance effect specific to the material of this layer and from the so-called spin transfer effect (known as “spintorque”) which ensures compensation for the diverse losses in the material. Without the spin transfer effect, the oscillation of the magnetization vector would be damped and would dwindle progressively. Sustained by virtue of the spin transfer, the oscillation may be detected through the giant magnetoresistance effect. It is known to produce oscillators based on junctions having giant magnetoresistance effect. They can have applications in radiofrequency communications.
One of the advantages of oscillators using a junction having giant magnetoresistance effect is the very low bulk, the very high frequency of oscillation possible (for example from 5 GHz to 20 GHz), and the very broad band of adjustment of possible oscillation frequencies (through action on the current crossing the junction).
But the main drawback of these oscillators is the very low power of the signal available at output. Their frequency stability is moreover not excellent and in general they exhibit phase noise that it would be preferred not to have.
It has already been proposed to improve the frequency and to increase the power of the output signal by coupling several oscillators in such a way that they operate in synchronism with one another.
U.S. Patent Application Publication No. 2009/0115541 gives an example thereof. The junctions are coupled by a resistor. It has been noted that the phase noise and the resistance to disturbances of the oscillation were not as good as would be hoped. The disturbances envisaged here are disturbances originating from outside the oscillator: for example, in an application to a portable telephone, the disturbances may originate from the changes of magnetic or electrical environment depending on where the telephone is located. It is desired that the oscillator remains synchronized despite these disturbances, or at least that it converges very quickly to a resynchronization. The oscillator of the mentioned publication does not allow sufficiently fast resynchronization. Moreover, if it is desired to increase the output power by placing several very low power oscillators in synchronism, it is further necessary that the oscillators be in phase, failing which the signals do not add together and may even subtract from one another. The devices of the prior art do not allow this phase alignment to be done correctly.